This option determines if the choice values should be translated and in which
translation domain.

The values of the choice_translation_domain option can be true (reuse the current
translation domain), false (disable translation), null (uses the parent translation
domain or the default domain) or a string which represents the exact translation
domain to use.

If the widget option is set to single_text, this option specifies
the format of the input, i.e. how Symfony will interpret the given input
as a datetime string. It defaults to the RFC 3339 format which is used
by the HTML5 datetime field. Keeping the default value will cause the
field to be rendered as an input field with type="datetime".

The internal normalized representation of this type is an array, not a \DateTime
object. Therefore, the data_class option is initialized to null to avoid
the FormType object from initializing it to \DateTime.

When you create a form, each field initially displays the value of the
corresponding property of the form's domain data (e.g. if you bind an object to
the form). If you want to override this initial value for the form or
an individual field, you can set it in the data option:

The data option always overrides the value taken from the domain data
(object) when rendering. This means the object value is also overriden when
the form edits an already persisted object, causing it to lose its
persisted value when the form is submitted.